JP-2007-32540A describes that an instant rotating speed (instant NE) of an internal combustion engine is measured based on a crank angle signal transmitted from a crank angle sensor and an actual torque of the engine is estimated based on the measured instant NE. Moreover, based on the estimated actual torque of the engine, various types of abnormalities can be detected.
For example, when bio-fuel is supplied to a diesel engine and unburned bio-fuel flows into a crankcase, the engine oil is diluted by the unburned bio-fuel, which may cause a situation where the engine oil flows into a combustion chamber of the engine. In this situation, the engine oil is burned in the combustion chamber, so that the actual torque of the engine is increased more than a torque originally assumed. Thus, it can be determined whether a malfunction occurs in the engine control system based on an increase in the actual torque. Also, when there is a malfunction in which a fuel injector unintentionally injects fuel, the actual torque of the engine is increased more than a torque originally assumed. Thus, it can be determined whether a malfunction occurs in the engine control system based on the increase in the actual torque.
Although it can be determined whether a malfunction occurs in the engine control system based on the actual torque, it is impossible to determine what type of malfunction occurs in the engine control system. That is, in both malfunction cases where the engine oil flows into a combustion chamber of the engine and where a fuel injector has a malfunction, the actual torque is increased. Although it can be determined that a malfunction occurs, it is impossible to determine which one of the malfunction cases occurs.